I am using the router in 3G/4G mode with a 3 mobile SIM card. It has been operating fine since March 2019, when we started using it, until 2 days ago when certain websites (Microsoft sharepoint among others) have been unable to load and just get timed out (with the same result on a Windows laptop, two Chromebooks and two smartphones), whilst other websites are not affected.

The problem is definitely with the router; we have taken the SIM card out and used it directly in a Windows laptop SIM slot and all websites load quickly and, using the laptop as a mobile hotspot, all other devices are able to load the sites without a problem through the SIM 4G connection. (The smartphones can also load all sites using their own mobile connection.) The problem only exists with the SIM in the TP-Link router and applies to the same sites across all devices.

The firmware is the latest available for the hardware. We have tried many reboots, even leaving it switched off for over an hour, but nothing has helped.

The DNS servers are set to 8.8.8.8 and 8.8.4.4  We haven't changed anything with the router from the time it was working fine to when it wasn't.

Has anyone had this problem and been able to solve it?